Traditionally, salt or acid solutions are pumped downhole to electrochemically degrade material in the frac ball (i.e., IN-Tallic®) to shrink the ball and pass it through the ball seat. However, this method is relatively slow and is not always possible due to adverse downhole conditions such as packing off of proppant above the seat.
IN-Tallic® is an electrochemically degradable material commonly used in frac balls and ball seats. When an electrolyte such as KC1 is pumped downhole, a galvanic corrosion reaction is initiated that degrades the frac ball or ball seat, eventually allowing the ball to be cleared from the seat. However, adverse downhole conditions can sometimes make it impossible to pump a salt or acid solution downhole to reach the degradable material. For example, proppant can build up above the ball seat, preventing the solution from reaching the frac ball. Additionally, depending on formation properties, operators may not want to add a large amount of salt or acid to the frac fluid. A high concentration of salt or acid solution (i.e., 10% KC1) is required at surface to achieve an adequate concentration (i.e., 2% KC1) at the frac sleeve, which may be 8,000 meters downhole in an offshore well.
The production ports of the upper sleeve of multi-sleeve tools have inserts filled with beads to provide screening of the production fluid. These inserts are known as bead-pack screens or bead screens. Such tools have several rows of production ports, each with several bead screens arranged along the circumference. In these tools a first sleeve is shifted to open treatment ports and then a second sleeve is shifted to open the screened production ports while closing the treatment ports.
In one aspect, the present invention presents a mechanically-actuated valve that allows the storage and release of fluid from a chamber inside a frac sleeve to degrade the frac ball or ball seat, allowing the ball to pass through the seat. The salt or acid solution is contained in a chamber inside the frac sleeve to ensure the solution will reach the degradable material. Pressuring up behind a seated ball causes the sleeve to shift and open a valve which releases the solution from an inner chamber into the fluid surrounding the frac ball. After the mechanical actuation of the valve, the released solution will initiate a galvanic corrosion reaction in the frac ball to degrade it and pass it through the seat.
A frac sleeve can be built with an inner chamber that is filled with a high-concentration salt or acid solution selected to electrochemically degrade the frac ball or seat. The chamber has a valve that is normally closed, containing the fluid inside the sleeve until activation. Once the ball is seated and pressure is built up, an inner sleeve is shifted. The shifting of the sleeve can either instantly open the valve to the inner chamber or initiate a timer to open the valve after a set time. Once the valve is opened, the salt or acid solution is released from the chamber into borehole, where it surrounds the frac ball and seat and begins the electrochemical degradation of the material. After enough material has been removed from the outside of the ball or inner wall of the seat, the ball will pass through the seat and subsequent operations such as production can be carried out.
The invention ensures the frac ball/seat will degrade even with adverse downhole conditions such as packing off of proppant above the seat; faster degradation of frac ball; elimination of delay from pumping down the salt or acid solution and/or reduced volume of salt or acid solution needed to degrade a ball. Placement in the sleeve reduces loss of concentration from pumping down fluid. Applications in a variety of tools that use degradable materials is envisioned.
Relevant art includes U.S. Pat. No. 8,573,295; 9,079,246 and US 20130146302.